TV and radio signals take over when GPS goes wrong

We all take GPS for granted: but what happens if we lose the signal or it's jammed?

BAE Systems has developed a positioning system that it claims will work even when GPS is unavailable. Its trick is to use the miasma of radio frequency signals we are all bathed in from TV, radio and cellphone masts, and even WiFi routers, to work out where we are.

GPS is a weak, highly jammable signal, equivalent, it is said, to trying to see a car's headlights from 20,000 kilometres away. And as New Scientist has revealed before, the availability of illegal handheld jammers online is indeed allowing people to block GPS signals.

Once jammed, a spoof GPS-format signal can be created to direct a vehicle (car, aircraft or ship say) in the wrong direction. Just two weeks ago, the radio navigation department at the University of Texas at Austin showed how an attacker could spoof GPS to force a small helicopter drone off course in a trial in a football stadium. And after a man died in May when an Austrian drone lost GPS and crashed in South Korea, the need for a backup positioning system became crystal clear - especially as drones prepare for mass civilian applications.

BAE's answer is dubbed Navigation via Signals of Opportunity (NAVSOP) and it interrogates the airwaves for the ID and signal strength of local digital TV and radio signals, plus air traffic control radars, with finer grained adjustments coming from cellphone masts and WiFi routers.

In any given area, the TV, radio, cellphone and radar signals will be at
constant frequencies and power levels as they are are heavily regulated
- so positions can always be triangulated from them. It's like the way
Google Maps on a cellphone uses local WiFi signals from homes and
offices to improve positioning calculations based on cellphone mast and
GPS signals.

"The real beauty of NAVSOP is
that the infrastructure required to make it work is already in place,"
says a BAE spokesman - and "software defined radio" microchips that run
NAVSOP routines can easily be integrated into existing satnavs. The firm
believes the technology will work in urban concrete canyons - where not enough GPS satellites can be "seen" by a receiver - and deep inside buildings where low power satellite signals cannot currently reach. As long as you can receive over-the-air TV or radio, you'll be able to find out where you are. At least, that's the theory.

Amusingly, perhaps,
BAE says that even the signals from GPS jammers (if they are on all the
time) can be used to build a radio frequency picture of an area. But the system will fall down, of course, if an extended power outage covers a wide area - and that's probably one reason BAE sees it as a complement to GPS, rather than a replacement. And Galileo, the EU's putative satellite positioning network, could equally become a natural backup for GPS. Similarly, there are many rival options for indoor positioning, too.

NAVSOP will
be demonstrated at the Farnborough International Airshow in the UK in the week of 9
July, where BAE hopes to show it calculating user locations to within a
few metres.

"especially as drones prepare for mass civilian applications"
Since when has there been intelligent drones preparing for anything?

Rodney
on June 29, 2012 3:44 PM

Dear BAE, because this method is so old and worthless, Ill offer it for free. Combine the idea of cheap home routers with 256 digital channels, with the autocorrelating LFSR (PRBS) encoding method used by GPS.

Hay presto, a $10 chip with ten thousand the times resiliancy of GPS, and at standard 2.54 Ghz, even at just single cycle coding, single channel reception, 10cm accuracy.

Even if Id tried to patent it, back in 1997, the legal arguments means it would be free to everyonewehn it expired in 5 years time anyway, so theres no point, its only worth so many billion dollars. That is, worthless.

Ramsey Faragher
on June 29, 2012 9:51 PM

NAVSOP actually makes use of timing, carrier phase and signal strength measurements - timing and carrier phase give good outdoor performance, and signal strength provides good indoor performance, but the more measurements, in any environment, the better.

Bill
on July 2, 2012 1:02 PM

Does that mean if my local radio announcer drops his coffee on the transmitter that my plane is going to crash?

Ramsey Faragher
on July 2, 2012 8:04 PM

Hi Rodney,

As I'm sure you are fully aware, transmitting any kind of meaningful power requires licences, and licences require money. Infrastructure requires maintenance, and so more money. If you suddenly want to start operating in a new country, you need more infrastructure, and you need to make it suddenly appear as if by magic the moment you need it. Your concept is certainly not free, it represents a massive investment in deployment and maintenance costs since you are talking about the deployment of new transmitters transmitting specific signals. NAVSOP exploits the tens of thousands of masts already in place in a given country, that someone else pays the licences for and maintains, and we get to make use of at zero cost.

Ramsey

Xiaoji Niu
on February 4, 2013 1:35 PM

Does this tech need frequent update of the maps of those Signal of Opportunity? And how?
It seems not feasible to be maintained by the service provider because of the cost and manpower. But it might be somehow updated by users.